The present invention relates to a method of manufacturing a plate for a battery electrode and the plate for a battery electrode manufactured by the method, and more particularly to the plate for an electrode which is preferably used for a supply battery of an electric car because of a great thickness thereof to increase the amount of an active substance to be applied thereto and because of a preferable contact thereof with the active substance applied thereto to prevent it from dropping therefrom.
Heretofore, generally, as the plate of an electrode for using a positive electrode and a negative electrode of a nickel/hydrogen battery, a nickel/cadmium battery or the like, principally, a pore-formed nickel-plated steel plate (hereinafter referred to as punching metal) formed by plating an iron plate on which pores are formed by punching is used. An active substance is applied to the punching metal to form the electrode. In the case of a cylindrical battery, the electrode comprising belt-shaped positive and negative electrodes is spirally wound through a separator to accommodate them therein. In the case of a rectangular or square battery, positive and negative electrodes are layered on each other through a separator to accommodate them therein.
The punching metal is used as the plate for a battery electrode by punching a flat cold-rolled steel plate having a thickness of 60 xcexcm-100 xcexcm to form thereon circular pores, the diameter of which is 1.0 mm-2.5 mm in a required pattern such that the open area percentage thereof is 40%-50% and then nickel-plating the steel plate to keep it resistant to corrosion.
As the plate of an electrode consisting of positive and negative electrodes of a lithium primary battery, mainly, a lath processed from metal such as SUS and Ti is used. The lath is charged with an active substance to form the electrode. In a lithium secondary battery, the active substance is applied in a required thickness to both surfaces of a metal core material made of an aluminum foil to form a positive electrode, and the active substance is applied in a required thickness to both surfaces of a metal core material made of a copper foil to form a negative electrode.
As the plate of an air electrode to be used as the positive electrode of an air zinc battery, mainly, a metal screen (nickel-plated SUS mesh) is used. As a zinc storage battery which attracts public attention recently as a car battery, a cast lattice or an expanded lattice consisting of lead alloy (Pb/Sb alloy, Pb/Ca alloy, Pb/Ca/Sn alloy or the like) is used. The active substance is applied to the screen and the lattice to form the electrode.
Further, in recent years, as the plate of the electrode of the nickel/hydrogen battery, the nickel/cadmium battery, and the lithium primary battery, porous metal sheets formed by chemically plating resinous foamed materials, nonwoven cloths or mesh materials to make them electrically conductive, and then electroplating them, and then, removing resinous materials and sintering them are also used.
Any of the above-described plates for a battery electrode are flat. An active substance is applied to both surfaces thereof to fill it into pores formed thereon and coat both surfaces thereof with the active substance in a required thickness. Because the above-described punching metal, the lath, and the metal screen are not three-dimensional, they are not in close contact with the active substance and thus have a low active substance-holding force. In particular, if they have large pores formed thereon, the active substance is likely to separate and drop therefrom during the manufacture and use of an electrode. In order to solve the problem, a method of adding a large amount of binder to the active substance to prevent it from separating and dropping from the plate is known. But when a large amount of binder is added to the active substance, the reactivity of the active substance deteriorates, and thus the battery characteristic is inferior.
The active substance is filled into pores of the foamed porous metal sheet having a three-dimensional structure. Thus, the porous metal material has a higher active substance-holding property than the punching metal and the metal screen. But in the foamed porous metal material, the skeleton thereof surrounding the pores is not thick. Thus, the foamed porous metal material has a low electricity-collecting performance, thus being incapable of accomplishing a rapid electric charge or discharge when a rapid electric charge or discharge is required.
Because any of the conventional plates for an electrode is thin, the active substance is thinly applied thereto in the thickness direction thereof. Therefore, the electrode has a low electrical conductivity in its thickness direction. Thus, it is difficult to improve the characteristic of the battery.
In order to solve this problem, in Japanese Laid-Open Patent Publications Nos. 7-130370 and 7-335208, there are proposed electrodes having an apparent thickness twice as great as that of a metal plate or a metal foil, including the thickness of burrs each formed on the periphery of each of pores formed on the metal plate or the metal foil by using upper and lower dies. However, when pores are formed by a pair of dies, the maximum open area percentage is about 50%. Further, it is difficult to form many fine pores on the entire surface of the metal plate or the metal foil by reducing the diameter of each pore and the pitch between the pores. Therefore, even though the burr is formed on the periphery of each pore, the burr has a low occupation percentage and an insufficient active substance-holding force. In addition, because the diameter of each pore is large, the active substance charged into the pores is likely to be dropped therefrom. Further, because the pitch between the pores is long, the area of the metal foil or the metal plate is great, which prevents movement of ions in the active substance. Thus, these electrodes cause batteries to have inferior performance. In order to solve these problems, it is conceivable to reduce the diameter of each pore and the pitch between the pores. But it is technically very difficult and very costly to form the pores by a pair of upper and lower dies as described above. Furthermore, only one metal plate having burrs formed thereon does not allow the application amount of the active substance to be increased so much.
The present invention has been made in view of the above-described problems. It is accordingly an object of the present invention to provide a method of manufacturing a plate for a battery electrode which holds an active substance thereon firmly and allows a large amount of the active substance to be applied thereto in the thickness direction thereof and provide the plate for a battery electrode manufactured by the method.
In order to solve the above-described problem, firstly, there is provided a method of manufacturing a plate for a battery electrode comprising the steps of: passing a thin metal sheet between a pair of embossing rotation rollers having concave portions and convex portions formed on a peripheral surface thereof to form concave portions and convex portions on an entire surface of the metal sheet, and form pores each on an apex of each of the concave portions and convex portions and generate burrs each projecting outward from a peripheral edge of each of the pores by a pressing force during formation of the concave portions and convex portions.
According to the above-described method, by merely passing the metal sheet between a pair of the embossing rotation rollers, comparatively fine concave portions and convex portions can be formed on the entire surface thereof, and at the same time, pores are each formed on the apex of each concave portion and convex portion, and the burr can be projected from the peripheral edge of each pore. Thus, according to the method utilizing the embossing method, compared with the conventional method of forming pores by means of upper and lower dies, the diameter of each pore which is formed on the apex of each concave portion and convex portion and the pitch between the concave portions and that between the convex portions can be allowed to be smaller. Therefore, the pitch between the pores each formed at the apex of each of the concave portions and convex portions can be reduced greatly and the open area ratio, namely, the ratio of the area of the pore to the area of the metal sheet can be allowed to be much larger than that of the metal sheet formed by the conventional method using the dies. Because the burr is generated at the apex of each of the concave portions and convex portions formed densely on the entire surface of the metal sheet, the ratio of the area of the burr to the area of the metal sheet can be allowed to be much higher than that of the metal sheet formed by the conventional method.
As described above, fine concave portions and convex portions are formed on the entire surface of the metal sheet, the pores are each formed on the apex of each concave portion and convex portion, and the burrs are each generated on the periphery of each of the pores. Thus, an active substance which can be applied to the metal sheet can be charged into the concave portions and the convex portions and held by the burrs each generated on the periphery of the apex of each of the concave portions and convex portions. Hence, the charge amount of the active substance can be allowed to be much greater than that of the active substance which is applied to the metal sheet by the conventional method. Further, the active substance can be held by the concave portions and the convex portions reliably because the portions are fine and also held reliably by the burrs because the burrs are present densely on the surface of the metal sheet. Thus, the force of holding the active substance can be allowed to be much greater than the force of holding the active substance which is applied to big pores formed at long pitches by the conventional die. In addition, because the open area ratio is high, ions of the active substance move actively, thus improving the performance of a battery.
More specifically, by forming the concave portions and convex portions on the metal sheet itself, the apparent thickness of the metal sheet can be allowed to be a desired thickness 3 to 500 times as large as that of the metal sheet. For example, when convex portions are formed upward and downward on the metal sheet having a thickness of 10 xcexcm to make the thickness thereof 4 mm, the apparent thickness thereof is 400 times as large as the thickness thereof.
Further, secondly there is provided a method of manufacturing a plate for a battery electrode comprising the steps of: passing a thin metal sheet between a pair of rotation rollers, one of which is an embossing roller having concave portions and convex portions formed on a peripheral surface thereof and a other of which is rubber roller having smooth outer surface, to form pores on the metal sheet and generate burrs each projecting toward one side from a peripheral edge of each of the pores by pressing the rubber rollers against the convex portions of the embossing roller.
According to the above-described second method, although clear concave portions and convex portions are not formed on the metal sheet itself, a large number of pores are formed on the entire surface thereof and a burr projecting in one direction (toward rubber roller) from each pore can be formed. Thus, when the burr is desired to be projected in only one direction, the second method can be preferably used.
Further, thirdly there is provided a method of manufacturing a plate for a battery electrode comprising the steps of: passing a thin metal sheet sequentially between first and second sets of rotation rollers each consisting of an embossing roller having concave portions and convex portions formed on a peripheral surface thereof and rubber roller having smooth outer surface to form pores on the metal sheet and generate burrs each projecting toward one side from a peripheral edge of each of the pores by pressing the rubber roller against said convex portions of the embossing roller when the metal sheet is passing between the embossing roller and the rubber roller of the first set; and passing the metal sheet between the embossing roller and the rubber roller of the second set to form pores on the metal sheet at different positions thereof and generate burrs each projecting toward the other side from the peripheral edge of each of the pores.
Further, fourthly, there is provided a method of manufacturing a plate for a battery electrode. In the fourth method, metal sheets of the same kind or different kinds, according to the first, second, and third methods, having the pores and the burrs each projecting from the peripheral edge of each of the pores are layered one upon another; and the burrs of an upper layer metal sheet and the burrs of a lower layer metal sheet adjacent to the upper layer metal sheet are interlocked with each other to integrate the upper layer metal sheet and the lower layer metal sheet with each other; and spaces between the upper layer metal sheet and the lower layer metal sheet are communicated with each other through the pores.
That is, the above-described xe2x80x9csame kindxe2x80x9d includes the case in which the plates described in the first method are layered one upon another or the plate described in the second method or the plate described in the third method are layered one upon another. The above-described xe2x80x9cdifferent kindsxe2x80x9d include the case in which the plate described in the first method and the plate described in the second method are layered one upon another or the plate described in the first method and the plate described in the third method are layered one upon another and the plate described in the second method is layered on the surface at both sides thereof.
In a metal sheet on which burrs are each formed on the peripheral edge of each of the pores by the first method through the third method, a large number of pores is formed by the embossing roll. Thus, the burrs each projecting from the peripheral edge of each pore are present on the substantially entire surface of the metal sheet. When these metal sheets are layered one upon another, the burrs are interlocked with each other and thus the metal sheets can be integrated with one another. Further, the metal sheets layered one upon another through the interlocking of the burrs do not make close contacts, but spaces are generated between layered metal sheets. The spaces communicate with one another through the pores. Thus, when an active substance is charged into the layered metal sheets, the active substance can be reliably charged between the metal sheets.
Further, the present invention provides a plate for a battery electrode manufactured by any one of the above-described methods.
Preferably, there is provided a plate for a battery electrode which is manufactured by the fourth method and comprises a metal sheet, according to the first method, having pores each formed on an apex of each of concave portions and convex portions and burrs each projecting outward from a peripheral edge of each of the pores and metal sheets, according to the second method, having burrs projecting toward one side. The metal sheets according to second method are layered on a surface at both sides of the metal sheet according to the first method and sandwiching the metal sheet according to the first method therebetween. The burrs are projected toward an inner surface side of the metal sheets according to the second method.
Preferably, there is provided a plate for a battery electrode comprises a metal sheet, according to the third method, having burrs each projecting toward both directions from a peripheral edge of each of the pores and metal sheets, according to the second method, having burrs projecting toward one side. The metal sheets according to second method are layered on a surface at both sides of the metal sheet according to the third method and sandwiching the metal sheet according to the third method therebetween. The burrs are projected toward an inner surface side of the metal sheets according to the second method.
Two burr-projected metal sheets may be layered one on the other to project the burrs outward from both sides thereof.
As the center plate sandwiched between the upper and lower plates, it is possible to use the plate manufactured by the first method such that it has a great thickness because of concave portions and convex portions formed thereon or the plate manufactured by the third method such that it has a great thickness because of burrs projected from both sides thereof so as to increase the charge amount of the active substance.
As the upper and lower plates, it is possible to use the plate manufactured by the second method such that it has burrs projected in only one direction so as to project the burrs inward not outward.
In particular, because the plate manufactured by the first method has fine concave portions and convex portions densely, the charge amount of the active substance can be increased and the active substance-holding force can be increased by filling it into the spaces surrounded with the concave portions and convex portions. Even one metal sheet has an increased application amount of the active substance. Thus, a plate consisting of a plurality of the metal sheets which are layered one upon another can be charged with more active substance. Further, the thickness of the plate for a battery electrode can be easily adjusted by merely adjusting the number of metal sheets which are layered one upon another. Thus, it is possible to provide the plate for a battery electrode which can be charged with a necessary amount of the active substance.
It is preferable to use a metal foil or/and metal sheet which is formed by rolling metal powder into a sheet. That is, a nickel foil, a copper foil, and an aluminum foil can be preferably used as a metal foil.
As the metal sheet which is formed by rolling the metal powder into a sheet, the metal sheet, formed by rolling the metal powder by a pattern roller, proposed by the present applicant and disclosed in Laid-Open Japanese Patent Publication No. 8-122534 can be preferably used. The metal sheet is formed by supplying metal powder to the peripheral surface of one pattern roller of a pair of pressure rollers, and then rolling the metal powder on the peripheral surface of the pressure roller directly by the rotation of a pair of the pressure rollers.
A metal sheet consisting of Ni, Al, Cu, Fe, Ag, Zn, Sn, Pb, Sb, Ti, In, V, Cr, Co, C, Ca, Mo, Au, P, W, Rh, Mn, B, Si, Ge, Se, La, Ga, Ir or an alloy of these elements can be preferably used the above-described metal sheet.
In the plate for a battery electrode manufactured by the first method, it is preferable to set the pitch between the concave portions and that between the convex portions to 0.5 mm-2.0 mm and the height of the concave portion and that of the convex portion to 0.1 mm-2 mm.
The present invention provides an electrode for a battery in which an active substance is charged into spaces in the plate for a battery electrode. In the electrode, because pores are each formed on the apex of each of fine concave portions and convex portions densely formed on the entire surface of the metal sheet, the pores are charged with the active substance and surrounded with the burrs each formed on the peripheral edge of each of the pores. Thus, the active substance hardly drops from the plate.
The active substance may contain an electrically conductive material. That is, with the increase in the volume of the active substance-application space surrounded with the metal sheets layered one upon another, the charge amount of the active substance increases. Normally, as the active substance does not contain an electrically conductive material, the electrically conductivity is a problem. Thus, it is preferable that the active substance contains the electrically conductive material when the volume of the active substance-application space is great and the active substance has a low electrical conductivity. Further, the present invention provides a battery having the above-described electrode for a battery. Because the electrode is thick and can be charged with a large amount of the active substance, it can be preferably used as the supply battery of an electric vehicle.